Experimental Study On Bearing Properties Of Rigid Pile Composite Foundation In Collapsible Loess Area Under Water Immersion Conditions

Collapsible loess is a special kind of soil.When it is soaked by water,the soil structure will be destroyed,the shear strength parameters will change,and a lot of collapsible settlement will occur under the action of the dead weight pressure of soil and the upper load.The collapsible settlement of loess makes the foundation not meet the requirements of bearing capacity,and seriously endangers the safety of construction structures.Composite foundation,as one of the treatment methods of collapsible loess foundation,can effectively reduce the settlement of foundation by making the pile and soil jointly bear the upper load.Meanwhile,the compaction of pile can eliminate the collapsibility of loess,give full play to the bearing potential of soil,and meet the requirements of bearing properties of foundation.In recent years,due to extreme weather events such as continuous rainfall makes the loess water phenomenon of composite foundation,after processing of composite foundation loess in the overlying water should not produce a large number of sedimentation leads to the shortage problem of bearing capacity,and existing some engineering in the use of rigid pile composite foundation processing collapsibility eliminated,infiltration depth,the settlement of pile foundation under the loess produces a large number of,As a result,the composite foundation does not meet the bearing capacity requirements and induces engineering problems.According to the above problem,this article,through the indoor model test,numerical simulation and analysis of engineering examples,in order to eliminate the collapsibility loess rigid pile composite foundation after sex as the research object,water analysis of collapsible loess region in rigid pile composite foundation loadbearing properties,the change rule of specification for improvement Suggestions,provide a basis for rational design in practical engineering and prevention measures.The main research work is as follows:(1)Through laboratory model test,the settlement of composite foundation during loading and soaking process is analyzed and studied.During the loading process,the settlement of loess composite foundation increases with the increase of load.After that,the immersion test under the condition of holding load is carried out,and it is found that the settlement increases exponentially due to immersion.The reasons are analyzed and the concrete measures should be taken when the adverse effects of immersion are brought about.(2)Through indoor model test,the changes of axial force of pile body,side friction of pile body,neutral point position and pile-soil stress ratio during loading and soaking are analyzed and studied.According to the test data,this paper summarizes and analyzes the change law of bearing behavior of rigid pile composite foundation in collapsible loess area under the condition of immersion,and puts forward that the adverse effects of foundation immersion should be considered in collapsible loess area based on the code.The code is refined and improved,and the calculation formula of negative friction is revised,which provides design basis for practical engineering.(3)Water based on collapsible loess regions in indoor model test of rigid pile composite foundation using ABAQUS finite element software established the threedimensional numerical model,simulation analysis of the collapsible loess region rigid pile composite foundation load-bearing character changes in the situation in the process of flooding,and the numerical simulation results and test results contrast analysis,It verifies the accuracy of laboratory model test and the feasibility of numerical simulation to study the variation law of bearing capacity of collapsible loess composite foundation.Then,by changing the different factors affecting the bearing properties of composite foundation,the corresponding measures to improve the additional settlement of composite foundation caused by flooding are studied,which is of guiding significance to practical engineering.(4)Combined with the engineering example,the settlement of concrete pile composite foundation in collapsible loess region is analyzed,and the field data and test data are compared and analyzed,which verifies the validity of the research content in this paper,and provides a reference for the subsequent similar foundation treatment design.